II. Field of the Invention
The present invention relates generally to the field of reciprocating pumps. More particularly, the present invention relates to an improved sealing cartridge for use in a reciprocating plunger pump which includes a high pressure seal, a low pressure seal, a vacuum seal, and an oil seal within a unitized cartridge assembly to facilitate servicing and/or replacing the various seals with minimal effort, and which provides improved sealing characteristics to prevent the unwanted migration of oil, fluid, and air during both priming and normal operating conditions.
III. Discussion of the Prior Art
Plunger pumps may be characterized generally as including a plunger which reciprocates past a plurality of stationary seals so as to generate a pressurized fluid flow. A necessary evil with plunger pumps is that the reciprocating action of the plunger generates friction with the various seals which, consequently, causes the seals to experience deterioration over time. In addition, seals are constructed of material having finite strength and resiliency characteristics such that the seals invariably deteriorate due to continued exposure to pressurized fluid. Deterioration of the seals reduces their ability to perform as intended, namely to prevent the migration of fluid between the various parts within the pump. Among other problems, seal deterioration may allow the fluid being pumped to seep into the lubricating oil found in the crankcase, thereby raising the specter of damaging the crankcase and/or crankcase components. Seal deterioration may also allow air to seep into the pumping chamber. The flow of air into the pumping chamber may disadvantageously result in air-lock during priming operations, and may cause unwanted cavitation during normal operation which adversely affects pumping efficiency. These and other negative ramifications of seal deterioration require that the seals within plunger pumps be changed periodically.
FIG. 1 illustrates a plunger pump 10 typical of those employed in the prior art. The pump 10 includes a crankcase 12, a head assembly 14, and a reciprocating plunger assembly 16. The crankcase 12 includes an oil chamber 18, a guide chamber 20 for slidably receiving a plunger guide 22, and a drainage area 24 open to ambient. The head assembly 14 is two-piece in construction, including a first head member 26 and a second head member 28. Extending between the first head member 26 and the second head member 28 is a retainer 30 for forcibly maintaining a seal spreader 32 and a high pressure seal 34 within the second head member 28. The second head member 28 further includes a retaining slot for fixedly retaining a low pressure seal 36 therewithin. The plunger assembly 16 includes a reciprocating plunger 38 coupled to the plunger guide 22 via a retaining nut 40 and a crankshaft 42 rotatably coupled to the plunger guide 22 via a connecting rod 44. In order to prevent the migration of oil from the crankcase 12, a cartridge 46 is provided extending between the second head member 28 and the oil chamber 18 having an oil seal 48 for forming an oil-tight junction about the plunger guide 22 and a wiper member 50 for augmenting the sealing capability of the oil seal 48. In the event that oil does seep past the wiper member 50 and the oil seal 48, a plurality of weep holes 52 are formed in the cartridge 46 to allow any oil to drain out of the pump 10 by exiting through the drainage area 24. In order to prevent the unwanted migration of fluid from the head assembly 14, the seal spreader 32 is employed in conjunction with the high pressure seal 34 to form a fluid-tight junction with the plunger 38 which is capable of maintaining high fluid pressure within the head assembly 14. The low pressure seal 36 is also provided within the second head member 28 to maintain a low pressure fluid bath against the plunger 38 for the purpose of cooling the high pressure seal 34.
While the pump 10 may be considered as generally effective, close examination will elucidate that the pump 10 is nonetheless fraught with several formidable drawbacks. First and foremost, the pump 10 fails to provide the various seals in a readily accessible and conveniently removable fashion such that servicing operations, such as seal repair and/or replacement, are laborious and time consuming. Indeed, the low pressure seal 36 is disposed completely within the confines of the second head member 28, the seal spreader 32 and the high pressure seal 34 are force fit in between the retainer 30 and the second head member 28, while the oil seal 48 is disposed within the far end of the cartridge 46. In this arrangement, a service person must thus remove the first head member 26, the retainer 30, the second head member 28, and the cartridge 46 to avail all of the sealing members for maintenance or replacement. This is particularly disadvantageous in that it is burdensome and time consuming to dismantle this hose of pump parts every time the seals require servicing. The task of servicing is furthermore made difficult due to the fact that the low pressure seal 36 is effectively buried within the second head member 28 which, as will be appreciated, requires substantial effort to remove and replace the low pressure seal 36. Another significant disadvantage stems from the configuration of the cartridge 46. More specifically, the cartridge 46 extends entirely within the crankcase 12 such that it may be difficult to obtain an adequate purchase on the cartridge 46 to extract it from the force fit position within the crankcase 12, thereby increasing the difficulty in servicing the oil seal 48. In addition, the oil seal 48 is disposed within the cartridge 46 without any type of restraining element between the oil seal 48 and the drainage area 24. This arrangement disadvantageously presents a likelihood that the oil seal 48 will become dislodged during operation, such as from excess friction between the oil seal 48 and the plunger guide 22 or from an increase in oil pressure within the crankcase 12.
A still further drawback is that the sealing arrangement permits air to migrate from the drainage area 24 into the head assembly 14 during priming operations and negative pressure conditions at the fluid inlet 54. This stems from the fact that the low pressure seal 36 is incapable of forming an adequate seal about the plunger 38 during such conditions. To further explain, the low pressure seal 36 is a standard U-cup which forms a unidirectional seal along the plunger when properly energized or expanded. The necessary energization occurs when low pressure fluid is allowed to flow between the low pressure seal 36 and the high pressure seal 34 such that the U-cup expands inwardly and envelops the plunger 38 to form a seal therealong. While the low pressure seal 36 is effective in minimizing the degree to which low pressure fluid may seep into the drainage area 24 when properly energized, air will nonetheless flow inwardly past the low pressure seal 36 during priming operations due to the fact that there is little or no fluid pressure to adequately bias the low pressure seal 36 against the plunger 38. This increases the likelihood of producing an air-lock condition within the head assembly 14 which may inhibit or altogether thwart priming operations within the pump 10. Negative pressure conditions at the fluid inlet 54 may occur, for example, when the fluid reservoir supplying coupled to the fluid inlet 54 is disposed below the pump 10. Such negative pressure also acts upon the low pressure seal 36 in that the fluid inlet 54 is coupled to the channel defined between the high and low pressure seals 34, 36. Negative pressure at the low pressure seal 36, in turn, causes the low pressure seal 36 to lose its charge such that air may be drawn therepast into the fluid inlet 54 and ultimately into the head assembly 14. During operation, such an influx of air into the fluid inlet 54 may cause cavitation which, as will be appreciated, adversely affects the efficiency and life expectancy of the pump 10.
In view of the foregoing deficiencies in the prior art, a need therefore exists for an improved seal arrangement within a plunger pump wherein all of the seals are maintained within a unitized cartridge assembly which is readily accessible and easily extractable for facilitating servicing operations. A further need exists for an improved seal arrangement wherein all of the seal members may be easily removed from a unitized cartridge assembly so as to minimize the effort in replacing the seals following removal of the cartridge assembly from the pump. A still further need exists for an improved seal arrangement wherein the oil seal is fixedly retained within the unitized cartridge assembly such that the oil seal will not become dislodged during operation due to excess friction between the oil seal and the plunger guide or from an increase in oil pressure within the crankcase. A yet further need exists for an improved sealing arrangement for a plunger pump which provides the ability to prevent airlock conditions during priming operations and cavitation due to negative pressure conditions at the fluid inlet during normal operation.